A new, kinematically anomalous HI component in the spiral galaxy NGC 2403

F Fraternali*, T Oosterloo, R Sancisi, G van Moorsel

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review


We discuss new, high-sensitivity H I observations of the spiral galaxy NGC 2403, which show extended emission at anomalous velocities with respect to the "cold" disk. This "anomalous" gas component (similar to1/10 of the total H I mass) is probably located in the region of the halo and rotates more slowly (similar to 20-50 km s(-1)) than the gas in the disk. Moreover, it shows a distortion in the velocity field that we interpret as a large-scale radial motion (10-20 km s(-1) inflow) toward the center of the galaxy. The most likely explanation for its origin and kinematics seems to be that of a galactic fountain. There is, however, a significant part of the anomalous gas that seems to be moving contrary to rotation and is difficult to understand in such a picture. These anomalous gas complexes discovered in NGC 2403 may be analogous to the high-velocity clouds of our Galaxy. They may be rather common in spiral galaxies and not have been detected yet for lack of sensitivity.

Original languageEnglish
Pages (from-to)L47-L50
Number of pages4
JournalAstrophysical Journal
Issue number1
Publication statusPublished - 20-Nov-2001


  • galaxies : halos
  • galaxies : individual (NGC 2403)
  • galaxies : ISM
  • galaxies : kinematics and dynamics
  • galaxies : structure
  • HALO

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